1. Field of the Invention
The present invention relates to hydraulic machines.
2. Description of the Prior Art
There are many different types of hydraulic machines that can be used to convert mechanical energy into fluid energy and vice versa. Such machines may be used as a pump in which mechanical energy is converted into a flow of fluid or as a motor in which the energy contained in a flow of fluid is converted into mechanical energy. Some of the more sophisticated hydraulic machines are variable capacity machines, particularly those that utilize an inclined plate to convert rotation into an axial displacement of pistons or vice versa.
Such machines are commonly referred to as swashplate pumps or motors and have the attribute that they can handle fluid under relatively high pressure and over significant range of flows. A particular advantage of such machines is the ability to adjust the capacity of the machine to compensate for different conditions imposed upon it.
The swashplate machines are, however, relatively complex mechanically with rotating and reciprocating components that must be manufactured to withstand large hydraulic and mechanical forces. These constraints lead to a reduction in the efficiency due to mechanical and hydraulic losses, a reduced control resolution due to the mechanical inefficiencies and the required size and mass of the components and a relatively expensive machine due to the manufacturing complexity.
In use as a variable capacity machine the swashplate is modulated to achieve a desired movement of component of a machine, either a position, rate of movement or applied force.
The movement of the swashplate is usually controlled by a valve supplying fluid to an actuator that acts through a compression spring on the swashplate. Control signals for the valve are generated from a set controller and a feedback, typically provided by a sensed parameter. In its simplest form the feedback may be provided by the operator who simply opens and closes the valve to achieve the desired movement or positioning of the component. More sophisticated controls however sense preselected parameters and provide feedback signals to a valve controller. The valve controller may be mechanical, hydraulic but more usually electronic to offer greater versatility in the control functions to be performed.
The control of the machine depends on the ability of the swashplate to adjust to the required movements with a high degree of fidelity. The swashplate assembly must, however, be capable of withstanding the high loads imposed on it by the mechanical and hydraulic forces generated by the machine and at the same time be responsive to control inputs. Typically, the swashplate is mounted on a pair of bearings at diametrically opposed locations. The use of roller and ball bearings reduces the friction opposing movement of the swashplate. However, the loads placed on such bearings may cause flexure of the swashplate between the bearings and consequent loss of precision.
It is therefore an object to the present invention to obviate or mitigate the above disadvantages.